The present invention relates to a cushion such as a bed mattress, a seat cushioning, a back rest cushioning or any other cushion where a support and cushioning of the entire or a part of a human or animal body is desired. The cushion is of a type using visco-elastic plastic foam material for suitably distributing the pressure from the body over a relatively large surface area of the body being cushioned by the cushion, such as a person lying on a mattress, a person seated in a couch or an animal resting on a veterinary surgeon""s table.
The visco-elastic foam assumes the formxe2x80x94in a somewhat xe2x80x9creluctantxe2x80x9d mannerxe2x80x94of the shape of the body, but when first it has been formed, it returns in a correspondingly xe2x80x9creluctantxe2x80x9d manner to its original form when the pressure from the body is removed, so that a stable support of the body is maintained. A definition of a visco-elastic foam may be the following: A solid ball such as a steel ball that is dropped vertically downwards from a height of 1 m and by gravity lands on a plane surface of the visco-elastic foam has a rebound vertically upwards of less than 10%, i.e., a rebound of less than 10 cm upwards from the plane surface of the visco-elastic foam.
The formed foam thus exercises only a modest elastic counter-pressure against that surface by which it is loaded, and for precisely this reason it will therefore allow the body to sink relatively deeply into the cushion in such a manner that this distributes its overall counter-pressure over a large area of the body, with a relatively uniform and relatively low counter-pressure per unit area of the supported area of the body.
Cushions such as mattresses of this type are preferred by many users, but the cushions are, however, intended especially to alleviate or counteract sores such as bedsores (decubitus) obtained from high-pressure points when lying on a mattress among those who are confined to their beds for long periods of time.
For practical use, however, it will be a precondition that an ordinary elastic layer exists under the overlying visco-elastic layer in order to counteract the deepest depressed parts in the overlying layer in order to provide an increased counter-pressure as a consequence of being pressed against a firm layer such as the bunk of a bed, the seat or the backrest of a chair or a couch. It is hereby known that in order to achieve a reasonably limited cushion thickness, a layer is arranged in the form of a highly-elastic foam layer or a spring base with mechanical springs which provides a suitable gradient with respect to supporting of the user.
However, this support layer must also have an appreciable thickness so that the elastic counter-pressure can be distributed in a suitable manner over the area of the cushion, without this having any extra strong effect precisely at the deepest depressed parts. The result is that in order to maintain a reasonably modest cushion thickness, compromised solutions have had to be found both outwards and inwards of the cushion, in that the thickness of the underlying, highly elastic layer has been minimized to such a degree that the desire concerning a uniform distribution of the counter-elastic forces has not been able to be fully satisfied. With regard to the upper surface of the cushion, it has been recommended that the cushion be supplemented with an overlying cover element in the form of a thin xe2x80x9ccomfort-providingxe2x80x9d plastic foam plate, which is easily elastic-compressible for final distribution of the counter-pressure on the body, but while still offering a degree of comfortable softness.
It is an object of the present invention to limit the poor pressure distribution of the highly elastic foam and to also avoid the lack of support that can be established by a cushion made of a material such as materials used for the overlying cover element. Thus, it is an object of the present invention to provide a high degree of support of the cushion irrespective of the weight distribution and of the entire weight of the person so that a more even pressure distribution is obtained of the cushion.
This object is obtained by a cushion where the cushion comprises an underlying layer consisting of a highly elastic polyurethane foam, at least a part of one side of the underlying layer being configured with at least one pattern of a non-plane surface, the mattress also comprising an overlying layer placed in abutment with the underlying layer, and said overlying layer being made of a visco-elastic foam.
With the present invention it has been found that it is possible to optimize a cushion of the relevant type, the cushion having, for example, a general thickness of between about 10 cm and 30 cm, preferably 15-20 cm, to offer a very high degree of pressure distribution without having points where the pressure is excessively higher than in other points. Accordingly, a high degree of user comfort of a lying person is offered.
According to the invention, this can be achieved by making use of a highly-elastic foam cushion plate, i.e., a plate element configured with a distinctly large non-plane upper surface. Certain users prefer to lie on such a surface, perhaps merely with separation with a sheet, i.e., resting against a number of coarsely distributed, conical-like or rib-like and substantially flexible raised portions.
By the present invention it has been realized that precisely such a surface on such a flexible plate element will constitute an ideal underlying layer for an overlying plate of the visco-elastic foam, in that such an underlying layer with a non-plane surface of any chosen shape will be able to display an ideal spring characteristic in supporting the overlying layer, which in itself will distribute and smooth out the direct counter-pressure from tops of the non-plane surface. The tops will thus not be effectual with regard to their original purpose, i.e., with regard to the xe2x80x9cpoint supportingxe2x80x9d of the body of the user, but rather on the contrary make it possible for the body of the user to be supported in a particularly uniform manner by use of the relevant underlying layer in relation to the visco-elastic overlying layer, and moreover without any of the layers needing to be particularly thick. A corresponding pressure distribution and comfort giving under support of the overlying layer cannot be achieved by use of a simple plate-shaped underlying part.
By the invention, a preferred feature is that the cushion is further configured with a relatively thin and soft top layer for integrated constitution of the overlying layer, so that the cushion can appear completely ready for use. This layer preferably also consists of visco-elastic foam material.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features.